This invention relates to spinal intervertebral fusion implants and method of making.
Of interest are commonly owned U.S. Pat. Nos. 6,277,149 and 5,507,872.
Surgical procedures for fusing adjacent vertebrae to treat various pathologies are well known. Implants for such procedures take a wide variety of shapes, forms and materials from bone to titanium inert materials, rigid and elastic, circular cylindrical, wedge shapes, cages with or without openings to accept bone fusion promoting material. The implants disclosed in the aforementioned copending applications is preferred. The implants are dimensioned and shaped to provide a predetermined disc space between the fused adjacent vertebra.
Generally, bone growth promoting material is used in conjunction with the implant especially inert implants of metal, ceramic or other synthetic compositions. Often this growth promoting material is in the form of bone chips or bone fibers. These are not normally load bearing materials. Ground up mineralized cortical bone may be used for such chips, but has little bone growth factors. If bone marrow is mixed in the composition, then bone growth factors become present. Such material may be taken from the patient for use in the implant for that patient. The bone source may be the illiac crest of the patient which is not desirable due to pain and long recovery periods.
C-shaped implants are described in Published PCT international applications WO 99/09914 and WO 00/24327 incorporated by reference herein.
U.S. Pat. No. 4,879,915 to Brantigan illustrates a spinal intervertebral implant. The implant is circular cylindrical and has a threaded bore and two opposing radial slots at one end for receiving an insertion tool threaded stud and prongs.
U.S. Pat. No. 4,904,261 to Dove et al. illustrates an inert C-shaped spinal fusion implant.
U.S. Pat. No. 5,192,327 to Brantigan discloses a prosthetic implant for vertebrae.
U.S. Pat. No. 5,443,514 discloses a method for fusing adjacent vertebrae using a spinal implant. The implant has through openings to provide for blood flow and bone growth from one side of the implant to the other side of the implant to adjacent vertebra. The implant is made of chopped fiber reinforced molded polymer, stainless steel or titanium. However, such materials do not permit direct bone in growth into the material and thus is a separate, discrete device which never forms a part of the bony structure of the spine except for the bone in growth in the through openings.
U.S. Pat. No. 5,522,899 to Michlelson discloses spinal implants which are substantially hollow rectangular configurations. In one embodiment, a series of implants are placed side by side in the intervertebral space to substantially fill the disc space. Autogenous bone material is packed within the hollow portion to promote bone growth. In other embodiments a substantially rectangular member has a series of ridges on upper and lower surfaces. The material of the implants is not described.
U.S. Pat. No. 5,7669,897 to Harle discloses a wedge implant having a first component of a synthetic bone material such as a bioceramic material and a second component of a synthetic bone material such as a bioceramic material or bone tissue or containing bone tissue in combination with other biointegration enhancing components. The second material is incorporated in accessible voids such as open cells, pores, bore, holes and/or of the first component. The first component forms a frame or matrix for the second component. The first component imparts strength to the second component. The first and second components can receive one or more pharmaceutical substances. The second component can fully or partially disintegrate upon completion of the implanting to promote penetration of freshly grown bone tissue into the first component.
U.S. Pat. No. 5,716,416 to Lin discloses insertion of an elastic intervertebral implant.
U.S. Pat. No. 5,720,751 discloses spinal insertion tools including a tool with opposing implant engaging portions and including a pusher assembly. In one embodiment the implant engaging portions are fixed and in other embodiments the insertion portion is formed of two arms secured in scissors-like fashion. A pusher may include a threaded stem for attachment to the handle for advancement of the pusher bar toward and away from the implant by rotation of the threaded stem.
U.S. Pat. No. 5,741,253 to Michelson, discloses a threaded self tapping spinal implant and insertion instrumentation. The implant is tubular and cylindrical and is inserted in an opening in the spine formed by a drill inserted in a sleeve.
U.S. Pat. No. 5,443,514 to Steffee discloses an instrument for holding and inserting a spinal implant and which includes an intermediate portion, a handle and a clamp portion. The implant is wedge shaped with two opposing flat parallel surfaces and two inclined surfaces which converge toward one end. The flat surfaces have recesses which receive the clamp of the instrument.
U.S. Pat. No. 5,782,830 to Farris discloses an implant insertion tool somewhat similar to the Steffee disclosure in that a pair of articulating jaws clamp an implant therebetween.
U.S. Pat. Nos. 5,885,299, 5,885,300, 5,910,141, 6,004,326, 6,033,405, 6,042,582 and 6,063,088 illustrate still other insertion tools for a spinal implant.
None of the above patents or applications address or recognize a problem with insertion of a C-shaped ramp or a femoral ring implant. In the C-shaped ramp, a side of the implant is C-shaped and open. During surgery, it is desired to fill the C-shaped opening with fusion promoting material such as bone chips to facilitate bone fusion of the adjacent vertebrae in a posterior insertion procedure. Also during this procedure, two side by side spaced implants may be inserted into the evacuated disc space between two adjacent vertebra. A small opening may be made on one posterior side of the spinal region.
As known, it is desired to fill the space around the implants with fusion promoting material such as bone chips and so on. However to fill the open space after the implants are inserted may be difficult. Even in those procedures where two openings are provided on each side of the spinal cord for separate implants in the posterior approach, a problem of filling the space with bone growth promoting material to promote fusion may be difficult due to the small space available. None of the above noted patents or applications are directed to this problem or offer a solution. Similar problems are present in ring shaped implants.
Another problem is that the C-shaped implant may break at the thinnest section upon insertion.
The present invention is a recognition of these problems and is directed to provide a solution.
A method of forming a fusion implant according to the present invention comprises forming a cortical bone into a discrete bone element having first and second opposing surfaces with a channel in communication with the opposing surfaces; forming a channel filling material of bone fibers; filling the interior channel with the fibers; demineralizing the fibers prior to or after the filling, and then securing the fibers to the discrete bone element. The filled channel thus strengthens the implant for insertion.
Preferably the securing step includes bonding the fibers to the discrete bone element. More preferably, the bonding step includes wetting the fibers prior to or after filling the channel and then drying the wet fibers. This ensures the filled channel retains the fibers without the use of additional elements.
In one aspect, the step of forming the channel filling material of bone fibers includes forming the fibers into a flexible sheet. This simplifies the assembly of the fibers to the implant channel.
In a further aspect, the sheet is formed into a spiral and the spiral is inserted into the channel further facilitating the insertion into the channel.
In a still further aspect, the forming the discrete bone element includes forming cortical bone into a C-shaped structure having a C-shaped cavity forming the channel and in a further aspect, the forming the discrete element includes forming cortical bone into a ring.
Preferably, the step of forming the channel filling material includes forming bone chips and/or powder of cortical bone and demineralizing the chips and/or powder prior to filling the channel.
In a still further aspect, the step of filling the channel includes filling the channel with wetted chips and the step of bonding includes drying the filled implant. The wet demineralized chips form a sticky substance for adhering to the discrete bone element when dried.
In a further aspect, the method includes forming the fibers into a flexible wet sheet, forming the sheet into a configuration generally matching that of the channel, filling the channel with the formed wet sheet and the bonding step includes drying the wet sheet in the channel.
Preferably, the method includes compacting the sheet in the filled implant, and more preferably, compacting the sheet by inserting a pin into the filled implant filling material.
A further aspect includes dividing the ring into two further implants each comprising a first bone element having a chamber open to three adjacent sides of the first bone element, forming the fibers into at least one flexible sheet and filling the chamber with the at least one flexible sheet.
In a still further aspect the step of securing the fibers to the first element includes wrapping the first element and at least one flexible sheet with a filament.
In a further aspect, the step of securing the fibers includes securing the at least one flexible sheet to the first element with a pin.
In a further aspect, the filling the channel step includes forming the fibers into at least one sheet of flexible fibrous material, wetting the fibrous material, wrapping the fibrous wet material about the first discrete element and then drying the wet material to bond it to the discrete bone element.
In a further aspect, a spinal implant for fusing together two adjacent vertebra of a human or an animal according to the present invention comprises a first discrete bone element of a first type of bone having opposing first and second sides extending between first and second end surfaces and a channel in communication with the opposing first and second sides intermediate the end surfaces, the first bone element exhibiting negligible bone growth factors, the bone for implantation between and engaged with adjacent vertebra. A second discrete fibrous bone element is formed of demineralized cortical bone fibers or powder, the second element for promoting bone growth between the adjacent vertebrae, the second bone element having a shape that is complementary to the channel for forming an integral implant unit with the bone of the first type. Means are provided for securing the first element to the second element.
In one aspect, the first element has third and fourth sides transverse the first and second sides, the channel being in communication with the third side to form a chamber open at the third side.
In a further aspect, the means for securing the first element to the second element comprises one of a bonding medium for bonding the elements to each other, a pin and a screw which passes into each element.
In a further aspect, the means for securing the first element to the second element comprises a filament.
In a further aspect, the first element has third and fourth sides transverse the first and second sides, the channel being in communication with the third side to form a chamber open at the third side, the second element forming a portion of the third side, the filament being wound about the end surfaces and the third and fourth sides.
In a further aspect, an annular groove is formed about the elements in the end surfaces and in the third and fourth sides.
Preferably the filament is one of a suture or animal tissue.
More preferably, the means for securing comprises molecular bonding.
In a further aspect, the first bone element has a given peripheral configuration, the second element comprising fibrous flex material having the configuration surrounding and abutting the first element in at least one plane.